Multipressure steam system for unfired combined cycle powerplant

ABSTRACT

An exhaust heat recovery steam generator is utilized exclusively to develop shaft power to drive a load and includes a high pressure evaporator, low pressure evaporator and deaerator evaporator positioned in that order in the exhaust stack and has provisions for providing deaerated feedwater to each evaporator. The deaerated feedwater is conducted through a split flow system to the low pressure and high pressure evaporator, and preferably also to the deaerator evaporator, to permit individual chemical treatment of the feedwater being provided exclusively to each evaporator so that deaerated and optimally chemically treated feedwater can be passed through each evaporator to abate corrosion and fouling therein. The feedwater is passed through each evaporator at a temperature above the condensation point of the exhaust gas passing thereover. All steam generated by the low pressure and high pressure evaporators is provided exclusively to a steam turbine to drive a shaft driven load and the deaerator evaporator providing steam solely to heat and deaerate the feedwater. The system is optimized in that the pressure levels for high and low pressure evaporators are optimized to produce the maximum practical steam turbine power from the energy in the gas turbine exhaust.

United States Patent 1 Rostrom 1 Nov. 6, 1973 MULTIPRESSURE STEAM SYSTEMFOR UNFIRED COMBINED CYCLE POWERPLANT [75] Inventor: Eric G. Rostrom,Marlborough,

Conn.

[73] Assignee: Turbo Power and Marines Systems,

Inc., Farmington, Conn.

[22] Filed: Mar. 22, 1972 [21] Appl. No.: 236,916

[52] US. Cl 60/106, 122/7, 122/401 [51] Int. Cl. F22d 1/00, F22b 37/48[58] Field of Search 122/448 B, 7, 401;

[56] References Cited UNITED STATES PATENTS 2,614,543 10/1952 Hood122/448 B 2,968,156 1/1961 Pacault 60/106 X 3,147,742 9/1964 May 122/73,150,487 9/1964 Mangan et a1. 60/39.18 B 3,325,992 6/1967 Sheldon60/39.l8 B 3,338,055 8/1967 Gorzegno et a1. 60/107 3,691,760 9/1972Vidal et a1 60/39.l8 B 3,703,807 11/1972 Rice (SO/39.18 B

Primary Examiner-Martin P. Schwadron Assistant Examiner-Allen M.Ostrager Attorney-Vernon F. Hauschild T ge 7 mm a [5 7] ABSTRACT Anexhaust heat recovery steam generator is utilized exclusively to developshaft power to drive a load and includes a high pressure evaporator, lowpressure evaporator and deaerator evaporator positioned in that order inthe exhaust stack and has provisions for providing deaerated feedwaterto each evaporator. The deaerated feedwater is conducted through a splitflow system to the low pressure and high pressure evaporator, andpreferably also to the deaerator evaporator, to permit individualchemical treatment of the feedwater being provided exclusively to eachevaporator so that deaerated and optimally chemically treated feedwatercan be passed through each evaporator to abate corrosion and foulingtherein. The feedwater is passed through each evaporator at atemperature above the condensation point of the exhaust gas passingthereover. All'steam generated by the low pressure and high pressureevaporators is provided exclusively to a steam turbine to drive ashaftdriven load and the deaerator evaporator providing steam solely toheat and deaerate the feedwater. The system is optimized in that thepressure levels for high and low pressure evaporators are optimized toproduce the maximum practical steam turbine power from the energy in thegas turbine exhaust.

13 Claims, 5 Drawing Figures i a i wC-lh 6) Patented NM, 1973 3,769,795

2 Sheets-Sheet 1 F IGJ MULTIPRESSURE STEAM SYSTEM FOR UNFIRED COMBINEDCYCLE POWERPLANT BACKGROUND OF THE INVENTION 1. Field of the InventionThis invention relates to mechanism for generating steam at multiplepressures and more particularly to such a system wherein deaerated andoptimally chemically treated feedwater is provided to the low pressureand high pressure evaporators so as to prevent corrosion therein andwherein fluid is passed through the evaporators at a temperature abovethe condensation point of the exhaust gas being passed thereover andwherein all the steam generated therein is conducted to a steam turbinewhich is mounted to drive a shaft driven load. A low pressure deaeratorevaporator or boiler is used in a downstream station of the exhauststack to generate low pressure steam to deaerate the feedwater and thefeedwater is then pumped by a boiler feedwater pump, positioneddownstream of the deaerator, in a split flow path so that the boilerfeedwater which is being'directed exclusively into the low pressureevaporator can be optimally chemically treated, as can the boilerfeedwater which is being directed exclu sively into the high pressureevaporator. In such a system allof the steam so generated is utilized ingenerating the shaft power to drive the load, and performs no auxiliaryfunction except during start-up and very low load operation.

2. Description of the Prior Art Multiple pressure steam generatingsystems are known, for example, in US. Pat. Nos. 1,883,194; 2,443,547;2,663,144; 3,147,742; 3,150,487; 3,177,659 and 3,304,712, but the priorart does not utilize steam so generated exclusively for developing shaftpower to drive a load, does not split the flow of feedwater to thedifferent evaporators or boilers, thereby permitting optimal chemicaltreatment thereof before entering the boiler to abate corrosion andfouling and does not teach an optimally designed system for maximumefficiency, while abating both internal and external corrosion of theboiler parts.

In the prior art, such as in U.S. Pat. No. 3,150,487, a very largecondenser is used to do its own deaerating but not as efficiently aswould be hoped. Thereafter, the poorly deaerated water was pumpeddirectly from the condenser to the low temperature economizer and lowpressure evaporator, it was necessary to add various purifying chemicalsthereto so as to prevent system clogging and other undesirable results.This created a very bad chemical situation in that these chemicals mustnot only operate properly for the low pressure evaporator condition butalso for the high pressure evaporator condition, and no known chemicalcompositions are capable of operating well under these two differentsets of conditions. The result was poor chemical purification of thefeedwater. The result is that chemical purification of the feedwatertakes place in only one of the evaporators, and because of thecompromise which must be made between the operating requirements and theoperating conditions of the low pressure and high pressure evaporators,the purification is less than optimum, resulting in a build-up of thesystem clogging impurities. To remove these impurities from the priorart construction required excessive system blow-down and this excessiveblow-down required the addition of makeup water to the condenser, tothereby cause further deaeration problems to the condenser. 7

SUMMARY OF THE INVENTION A primary object of the present. invention isto teach a waste heat steam generating system which can be used with acombined cycle gas turbine and steam turbine powerplant and whichutilizes the energy of the steam so generated exclusively to generateshaft power for the powerplant.

It is a further object of this invention to teach such a system whereinthe feedwater being provided to each evaporator can be optimallychemically treated and deaerated so as to minimize internal boiler andpump corrosion and fouling, so that feedwater or feedwater generatedfluid is passed through each evaporator at a temperature so as to raisethe heat exchanger evaporator coils above the condensation or dew pointof the stack gases, such as turbine engine exhaust gases, being passedthereover.

It is still a further object of this invention to teach such a systemwherein the system is optimized for maximum efficiency.

Other objects and advantages of the present invention may be seen byreferring to the following description and claims, read in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION or THE DRAWINGS DESCRIPTION OF THE PREFERREDEMBODIMENT Referring to FIG. 1 we see my multiple pressure generatingsteam system 10 used as part of a combined gas turbine-steam turbinecycle wherein the exhaust gases from gas turbine engine 12 are passed.through exhaust stack or duct 14 to provide the heat necessary to heatthe feedwater being passed through exhaust heat recovery or stack boilersystem 16 so as to generate the ,steam to drive steam turbine 18. Steamturbine 18 is shaft connected to drive load 20, which could be anelectric generator or other device. Gas turbine engine l2may bemechanically connected to steam turbine 18 through conventionalconnection 15 so that the turbines cooperate to drive load 20, but suchis not necessary. While a gas turbine engine 12 is shown to provide theexhaust stackheat to the exhaust heat recovery boiler 16, it will beevident to those skilled in the art that other mechanisms could performthis function.

In the FIG. 1 system, feedwater from condenser 22 is pumped bycondensate pump 24 through conduit 26 into deaerator 28. The initialfeedwater which enters deaerator 28 is discharged from the deaeratorthrough conduit 30 and then pumped by boiler feed pump 32 throughconduit 34, which splits into conduits 36 and 38 so that the portion ofthefeedwater from pump 32 which passes through conduit 36 entersdeaerator evaporator or boiler 40 exclusively and in passing through thecross tubes 41 thereof, which extend across exhaust duct 14, generatelow pressure saturated steam at a pressure whose saturated temperatureis above the condensation (or dew point) of the exhaust gases which isextracted through line 42 and directed back into deaerator 28 so as toheat the feedwater entering the deaerator through line 26, therebyliberating all noncondensable gases and air in the feedwater fordischarge to atmosphere. Preferably, deaerator 28 is of thefluid-tofluid type wherein the feedwater is sprayed through the steamentering deaerator 28 to form a saturated mixture at a temperature abovethe condensation temperature (or dew point) of the exhaust gases passingthrough the high pressure boiler. Accordingly, after systems start-up,deaerated feedwater is passed from the deaerator 28 to'the boiler feedpump 32 for distribution to the evaporators of exhaust heat recoveryboiler 16. Deaeration is desirable so that the feedwater is of minimalcorrosiveness to the metal of the boiler system through which it passes.

The pressure at the boiler feed pump 32 is the highest pressure in theboiler system and is sufficient to satisfy the pressure requirements ofthe high pressure evaporator. Pump 32 provides deaerated feedwater tothe entire system 16, including the deaerator just described. Theportion of the deaerated feedwater which passes through conduit 38passes through low temperature economizer 44, which is of conventionaldesign, so as to heat the feedwater before it leaves the low temperatureeconomizer 44 through conduit 46. The feedwater from conduit 46 splitsinto conduits 48 and 50. Approximately one-fourth to one-third of thefeedwater passing through conduit 46 passes through conduit 48 andtherefrom into low pressure evaporator 52 at a temperature above thecondensation point of the exhaust gas passing over the cross tubes 53 ofevaporator 52. It should be noted that the feedwater passing throughconduit 48 flows exclusively into low pressure evaporator 52 forevaporation therein and so that all steam is extracted therefrom throughconduit 54 and directed to a low pressure station in steam turbine 18.The ad vantage of having all of the feedwater passing through conduit 48flow exclusively into the low pressure evaporator 52 is that preciselythe proper chemical treatment can be madethereto by conventionaltreatment apparatus 57, to further reduce the harmful effect of thefeedwater upon the boiler parts which it flows through. Treatmentmechanisms 37, 57 and 59 preferably inject the required chemicalsdirectly into evaporator steam drums 45, 55 and 65, respectively, andare conventional.

Approximately two-thirds to three-fourths, depending on the gastemperature leaving the turbine exhaust, of the feedwater from conduit46 then passes through conduit 50 at approximately the temperature towhich it was raised in low temperature economizer 44 and is chemicallytreated in conduit 50, and preferably in boiler 65, by a conventionalchemical treatment mechanism 59, similar to mechanism 56, and then flowsas treated feedwater through the high temperature economizer 60 into thehigh pressure evaporator 62. It is important to note that all of thefeedwater which flows through conduit 50 and the high temperatureeconomizer 60 flows exclusively through conduit 61 into the highpressure evaporator 52 after being optimally treated chemically bychemical treatment mechanism 59. High temperature economizer 60 raisesthe temperature of the feedwater and hence the evaporator cross tubes 63above the condensation temperature of the stack gases passing thereover.All steam is extracted from the high pressure evaporator 62 throughconduit 64 and is then passed through conventional superheater 66 andconduit 68 to a high pressure station 70 in steam turbine 18. It willtherefore be seen that the superheated steam from high pressureevaporator 62 and the steam from low pressure evaporator 52 is admittedto steam turbine 18 at selected pressure stations in the steam turbineso that both work to power the steam turbine and generate shaft powerexclusively therein to drive shaft driven load 20. The superheated steamfrom conduit 68 expands and reduces in pressure in going through thehigh pressure portion 70 of turbine 18 and is of substantially the samepressure as is the steam entering turbine 18 from low pressureevaporator 52 via conduit 54 when the two join in mixing chamber orconduit 72 prior to passing through the low pressure portion 74 of thesteam turbine 18. After the mixed steam is expanded and reduced inpressure in passing through low pressure turbine portion 74, it passesthrough conduit 76 to conventional condenser 22 for recycling.Economizers 44 and 60 serve to heat the feedwater passing therethroughso that the feedwater which passes therefrom into evaporators 52 and 62,respectively, is essentially at the saturation temperature of steam insteam drums for 52 and 62 thereby maximizing the amount of steamgenerated therein. It will accordingly be seen that due to theindividual chemical treatment and deaeration of the feedwater passingthrough the evaporators, the interior of the boiler system is protectedoptimally, while the elevating of the temperature of the fluid passingthrough the tubes of the low temperature economizer prevents corrosivecondensation thereagainst by particles in the turbine engine exhaust gaspassing through stack 14 of heat recovery boiler 16. The system shown inFIG. 1 is a three pressure system in that there are three operatingpressures of feedwater and/or steam in my system.

Pressure reducing valves 39 and 56 serve to regulate the pressure of thefeedwater being passed through evaporators 40 and 52, respectively, aswell as regulate flow to these systems. Regulating valve 58 is aconventional feedwater regulating valve which regulates the flow toevaporator 62.

It will therefore be seen that all of the feedwater pass- I ing throughconduits 36, 48 and 61, respectively, flow exclusively into deaeratorevaporator 40, low pressure evaporator 52 and high pressure evaporator62, respectively. Therefore optimum chemical treatment can be metered toeach pressure system according to its individual and unique needs.

about 900 psia, the low pressure evaporator 52 operates at about 150psia and the deaerator evaporator 40 operates at about psia when theexhaust temperature is 850F. These are the three pressures of my system.Inthe prior art systems, which do not have a deaerator evaporator, someof the generated steam has to be utilized to perform the function offeedwater deaeration at some station between the condensate pump 24 andthe boiler feed pump32.

A substantial advantage to be gained by this three pressure system isthe control which is available over operating temperatures of the steamand water in the heat exchanger system 16. Specifically, the operatingtemperatures of the feedwater or generated steam are sufficiently highthat as the sulphur laden exhaust gases from turbine engine-12 passesthrough exhaust stack 14 and over the steam or water filled finnedcross-over tubes of heat exchanger system 16, such as the tubes 63, 53and 41 of the evaporator 62, 52 and 40, and the superheater 66, andeconomizers 60' and 44, the heated water passin'g'therethrough heats thetubes above the condensation or dew point of these sulphur particles andtherefore the moisture does not deposit or condense upon the metallicsurfaces of heat exchanger 16. The condensed water would provide themechanism for forming sulphuric acid which is highly corrosive so thatthe life of the entire system is adversely affected by deposit thereofon the metallic parts of boiler 16.

In my system shown in FIG. 1, by utilizing deaerator evaporator 40, wecan use fluid-to-fluid deaerator 26 and then position the boiler feedpump 32 between the deaerator 28 and the low temperature economizer 44so as to pump the deaerated feedwater to the two evaporators 52 and 62through a split flow system so that a selected portion of the feedwaterentersdeaerator 52 exclusively and can be optimally chemically treatedfor the condition therein, while the remainder of the feedwater entershigh pressure evaporator 62 exclusively and can be optimally treated forthe condition therein.

This permits us to satisfy the sensitive chemical puri ficationrequirements of each evaporator. a

For the purpose of more specifically describing the operation of mysystem shown in FIG. 1, attention will now be'directed to FIGS. 2 and 3,which are a temperature energy diagram for the heat recovery boiler 16and a temperature-entropy diagram for the steam cycle, re spectively.Thecondensate is pumped to the deaerator 28 at station (I) by thecondensate pump 24 at station (H). At the deaerator 28, the condensatemixes with saturated steam which passes from the deaerator evaporator 40into deaerator 28 through conduit 42. The

steam-water mixture leaving deaerator 28 through conduit 30 is asaturated liquid at station (J). All the feedwater is then pumped byboiler feed pump 32 at station (K) to a'pressure required by the highpressure evaporator 62.'The effect of the pump work is shown in FIG. 3at point (H) and (K) and has been exaggerated for illustrative purposes.Some of the feedwater is recircu- Iated back to the deaerator.evaporator 40,,and in particular the steam drum thereof at station (M),by passing through a pressure reducing feedwater regulating valve 39 atstation (L). The remainder of the feedwater passes through the lowtemperature economizer 40 to station (0). The feedwater'has been heatedin passing through low temperature economizer 44 to the saturationtemperature ofthe low pressure evaporator 52. Approximately one-quarterto one-third of the flow at station (0) passes through pressure reducingfeedwater regulating valve 56 at station (P) to the low pressureevaporator steam drum at station (Q). The remainder of the feedwatermixture passes through a third feedwater regulating valve 58 at station(S) to the high temperature economizer 60 where it :is heated to thesaturation temperature of the high pressure evaporator 62. In otherinstallations or under different operating conditions, the flow splitbetween ev'aporators 52 and 62 will be different. The steam evaporatedin 'the high pressure evaporator 62 is superheated insuperheater 66 inpassing from station (U) to (V). The high pressure, superheated steam,which we will call primary flow, enters the steam turbine 18 at thethrottle inletat station (W). This flow expands to station (X) to apressure approximately the same as the pressure in the low pressureboiler or evaporator 52. The steam generated in the low pressureevaporator 52, which we will call secondary flow, passes out of thesteam drum thereof at'station (R) and enters the steam turbine at theinduction point (Y), where it mixes with the primary flow at station(Z). The mixed flow of primary and secondary flow fluids then expandsdown to the exhaust pressure at station (AB) and is condensed tosaturated liquid in the condenser 22 at station (AB). The encircled orbracketed letters are utilized in FIGS.- 1 through 3 since they lendthemselves to describing the graphs of FIGS. 2 and 3 and theirrelationship to the system shown in FIG. 1.

My system 10 lends itself to use with other types of deaerators, forexample the types shown in FIGS. 4 and 5. The remainder of the systemshown in FIG; 1 is applicable to the FIGS. 4 and 5 constructions andcorresponding reference numerals will be used in describing the FIG. 4and 5 constructions as were used for the FIG. 1 construction.

Referring to FIG. 4 we see that condensate from pump 24 passesthroughconduit 26, including pressure regulating valve 39, intodeaerator 28'. Saturated steam from the deaerator evaporator 40 alsopasses through conduit 83 into deaerator 28' wherethe steam andfeedwater mix in Iiquid-to-liquid fashion to deaer ate the feedwater.The resulting mixture is saturated liquid at the deaerator pressure. Allof the mixture flow passes down through connecting pipel80, the exit ofwhichis always submerged below the water level in the deaeratorevaporator steam drum 43. The feedwater required to supply the;high and.low pressure system shown in FIG. 1 passes through conduit 30 to theboiler feed pump32, from which it is pumped in the fashion shown in FIG.1 to the low temperature economizer, low temperature evaporator, hightemperature economizer and high temperature evaporator and superheaterto the steam turbine. The remaining flow is mixed with the fluid in'thesteam drum 41 and joins the circulation system in the deaeratorevaporator 28'-40.

Now referring to FIG. 5 we see another deaerator embodiment which can beused with my system 10 otherwise depicted in FIG. 1. Inthisconfiguration, the condensate from condensate pump 24 is pumped fromconduit 26 into deaerator 28". There it mixes in fluidto-fluid'fashionwith the saturated steam from thedeaerator evaporator 40 being passedinto the deaerator 28" through conduit84. The saturated mixture'fromdeaerator 28 passes through conduit 30 and splits so that a portionthereof recirculates back to the deaerator evaporator 40 through conduit86, while the remainder thereof passes through conduit 88 to the boilerfeed pump 32. It will be noted that in the FIG. embodiment, chemicaltreatment mechanism 90 is placed in conduit 86 or in the steam drum ofdeaerator evapo-- rator 40 so as to optimally treat the feedwaterentering the deaerator evaporator 40, independently of the remainder ofthe feedwater system. The feedwater, in both the FIG. 4 and FIG. 5construction, will be treated independently at the low pressureevaporator steam drum and high pressure evaporator steam drum as shownin the FIG. 1 construction.

I wish it to be understood that I do not desire to be limited to theexact details of construction shown and described, for obviousmodifications will occur to a person skilled in the art.

I claim:

l. A combined gas turbine-steam turbine cycle powerplant wherein theexhaust gases of the gas turbine provide all of the heat to the steamboiler to generate steam for the steam burbine which is connected todrive a shaft driven load including:

A. a gas turbine engine,

B. a steam turbine engine,

C. an exhaust stack boiler through which the gas turbine engine exhaustgases are passed and including:

1. an exhaust stack positioned so that the exhaust gases from said gasturbine engine pass therethrough and having an exhaust gas inlet end andan exhaust gas outlet end,

2. steam generating means operatively associated with said exhaust stackincluding:

a. a superheater having tubes extending across said exhaust stackclosest said exhaust gas inlet end,

b. a high pressure evaporator having tubes extending across said exhauststack next downstream of the superheater,

c. a high temperature economizer having tubes extending across saidexhaust stack next-downstream of said high pressure evaporator,

d. a low pressure evaporator having tubes extending across said exhauststack next downstream of said high temperature economizer,

e. a low temperature economizer having tubes extending across saidexhaust stack next downstream of said low pressure evaporator, and

f. a deaerator evaporator having tubes extending across said exhaust gasstack next downstream of said low temperature economizer,

D. means to pass feedwater through said steam generating means includingthree feedwater flow path conduit systems including:

1. a first flow path conduit system directing a first selected quantityof feedwater exclusively to the deaerator evaporator at a selectedtemperature so that the feedwater being passed through said deaeratorevaporator is above the temperature of the condensation point of theexhaust gases passing over the deaerator evaporator,

2. a second flow path conduit system passing a second selected quantityof feedwater exclusively through said low temperature economizer andthen into said low pressure evaporator so that the temperature of thefeedwater being passed through both is above the condensation point ofthe exhaust gases being passed thereover, and

- 3. a third flow path conduit system directing a third selectedquantity of feedwater from said low temperature economizer exclusivelythrough said high temperature economizer and said high pres- 5 sureevaporator such that the temperature of the feedwater passing throughboth is above the condensation point of the exhaust gases passingthereover,

E. means to extract steam from said high pressure evaporator and pass itthrough said superheater and conduct said superheated steam to a highpressure station in the steam turbine,

F. means to extract steam from said low pressure evaporator and directit to a low pressure station in said steam turbine so as to cooperatewith said superheated steam to power said steam turbine to drive saidshaft driven load, and

G. means to add selected quantities of water purifying chemicals to theselected quantity of feedwater introduced exclusively to the deaeratorevaporator, to the selected quantity of feedwater being directedexclusively to the low pressure evaporator, and to the selected quantityof feedwater being directed exclusively to the high pressure evaporator,respectively.

2. A powerplant according to claim 1 and including:

A. a condenser connected to said turbine to receive steam therefrom forcondensation therein,

B. a feedwater deaerator positioned between said condenser and saiddeaerator evaporator, and

C. a boiler feed pump positioned between said deaerator and said threefeedwater flow path conduit systems so as to pump deaerated boilerfeedwater therethrough.

3. An unfired, waste-heat-steam turbine cycle powerplant whereinwaste-heat provides all of the heat to the steam boiler to generatesteam for the steam turbine which is connected to drive a shaft drivenload includ- 40 ing:

A. a steam turbine,

B. a waste-heat stack boiler through which the wasteheat is passed andincluding:

1. a waste-heat stack positioned so that the waste- "heat passesfiierethrough and having an inlet end and an outlet end,

V l. s team g eneratinggigans operatively associated with said waste-heat stack including:

a. a superheater having tubes extending across said waste-heat stackclosest said inlet end,

b. a high'pressure evaporator having tubes extending across saidwaste-heat stack next downstream 'of the superheater,

c. a high temperature economizer having tubes extending across saidwaste-heat stack next downstream of said high pressure evaporator,

d. a low pressure evaporator having tubes extending across saidwaste-heat stack next downstream of said high temperature economizer,

e. a low temperature economizer having tubes extending across saidwaste-heat stack next downstream of said low pressure evaporator, and

f. a deaerator evaporator having tubes extending across said waste-heatstack next downstream of said low temperature economizer,

5. A powerplant according to claim 4 and including means to deaerate thefeedwater to be passed through ond selected quantity of feedwaterexclusively through said low temperature economizer and then into saidlow pressure evaporator so that the temperature of the feedwater beingpassed through both is above the condensation point of the waste-heatgases being passed thereover, and -3. a third flow path conduit systemdirecting a third selected quantity of feedwaterfrom said lowtemperature economizer exclusively through said high temperatureeconomizer and said high pressure evaporator such that the temperatureof the feedwater passing through both is above the condensation point ofthe waste-heat gases passing thereover,

, D. means to extract steam from said high pressure evaporator and passit through said superheater and conduct said superheated steam to a highpressure station in the steam turbine,

E. means to extract steam fromsaid low pressure evaporator and directit-to a low pressure station in said steam turbine so as to cooperatewith said superheated steam to power said steam turbine to drive saidshaft driven load, and

. F. means to add selected quantities of water purifying chemicals tothe selected quantity of feedwater introduced exclusively to thedeaerator evaporator, to the selected quantity of feedwater beingdirected exclusively to the low pressureevaporator, and to the selectedquantity of feedwater being directed exclusively to the high pressureevaporator, respectively.

4. A multipressure steam generating powerplant including a heat recoveryboiler having:

h at t s n 1 2 m 92 n a da a;

stream end, B a high pressure evaporator having tubes in said'hastaiaarrs ussirsamsrsion, 3 C. a low pressure evaporator having tubesinsaid heat duct at a downstreamstation, D; first feedwaterconduit meansconnected to provide a selected quantity of feedwater exclusively tosaid low pressure evaporator and including: I

1. means to selectively chemically treat the feedwater so introducedinto the low pressure evaporator,

E. a second feedwater conduit means connected to provide a selectedquantity of feedwater exclusively to the high pressure evaporator andincluding:

1. means to selectively chemically treat the feedwater so introducedinto the high pressureevaporator, and

F. means to extract steam from both said low pressure evaporator andsaid high pressure evaporator.

said first and second conduit means.

6. A powerplant according to claim 5 wherein said feedwater deaerationmeans includes:

-A. a deaerator evaporator positioned in said heat duct downstream ofsaid low pressure evaporator, B. a fluid-to-fluid deaerator, and C.conduits connecting said deaerator to said deaerator evaporator toconduct feedwaterfrom said a l3 era t c 1 r to said deaerator evaporatorto generate low pressure steam therein and to conduct said steam back tosaid deaerator to heat and deaerate the entering feedwater. 7. Apowerplant according to claim 6,and including: A. means located in saidfirst feedwater conduit means to heat the deaerated feedwater'passing'therethrough to a point at which the deaerated feedwater will heat thelow pressure evaporator above the condensation temperature of thewasteheat gas passing thereover, and B. means located in said secondfeedwater conduit means to heat the deaerated feedwater passingtherethrough to a point at which the deaerated feedwater will heat thehigh pressure evaporator to a temperature above the condensationtemperature of the wasteheat gas passing thereover.

8. A powerplant according to claim 5 wherein said feedwater deaeratorincludes a fluid-to-fluid deaerator positioned externally of the heatstack and a deaerator evaporator having tubes in said heat stack at, astation downstream of said low pressure 'evaporator'and conduit meansconnecting said deaerator and said deaerator evaporator so that the lowpressure steam generated in said deaerator evaporator is directed tosaid deaerator so as to heat the feedwater entering the deaerator todeaerate the feedwater and so that the saturated mixture of feedwaterand steam accumulated in said deaerator after said mixing will be passedin part to said deaerator evaporator, in part to said low pressureevaporator and in part to said high pressure evaporator.

9 A gas turbine-steam turbine unt'n'ed, combined cycle powerplantwherein the exhaust gases of the gas turbine provide all of the heat'tothe steam boiler to generate steam for the steam turbine which isconnected to drive a shaft driven 'load including:

A. a gas turbine engine, B. a steam turbine engine, V Y C. a waste-heatboiler through which the-gas turbine engine exhaust gases are passed andincluding: i

1. an exhaust stack positioned so that the exhaust d. a low pressureevaporator having tubes extending acrosssaid exhaust stack nextdownstream of said high temperature economizer,

e. a low temperature economizer having tubes extending across saidexhaust stack next downstream of said low pressure evaporator, and

f. a deaerator evaporator having tubes extending across said exhaust gasstack next downstream of said low temperature economizer,

D. a condenser connected to said steam turbine to receive steamtherefrom for condensation therein,

E. a feedwater deaerator connected-to said condenser to receivecondensate feedwater therefrom,

F. a boiler feed pump connected to said deaerator to receive deaeratedfeedwater therefrom,

G. means to pass deaerated feedwater from said boiler feed pump throughsaid steam generating means and to said steam turbine including threefeedwater flow path conduit systems including:

selected quantity of deaerated feedwater exclusively to'the deaeratorevaporator from said boiler feed pump including:

a. a first conduit connecting said boiler feed pump to said deaeratorevaporator,

b. a second conduit conducting low pressure steam generated in saiddeaerator evaporator to said deaerator to serve as the deaerating steamand to be condensed therein for recycling as a saturated mixture throughsaid first and second conduits,

2. a second flow pathconduit system directing a second selected quantityof deaerated feedwater exclusively to the low pressure evaporatorincluding:

a. a first conduit extending between said boiler feed pump and said lowtemperature economizer through which a selected quantity of deaeratedfeedwater is passed to be elevated to a selected temperature above thecondensation temperature of the low temperature economizer'and the lowpressure'evaporator, f

. b. a second conduit connecting said low temperature economizer to saidlow pressure evaporator'to direct said second selected quantity ofdeaerated and selectively heated feedwater at a temperature above thelow pressure evaporator condensation point to the low pressureevaporator, and

c. a conduit connecting said low pressure evaporator to said steamturbine to direct all the steam generated in the low pressure evaporatorto said steam turbine,

. 3. a third flow path conduit system directing a third selectedquantity of deaerated feedwater from said boiler feed pump exclusivelyto said high pressure evaporator and including:

a. a first conduit connecting said boiler feedwater pump to said lowtemperature economizer,

b. a second conduit connecting said low temperature economizer to saidhigh temperature economizer in which the deaerated feedwateris heated toa temperature above the condensation temperature of said high pressureevaporator,

c. a third conduit connecting said high temperature economizer to saidhigh pressure evaporator so that the deaerated feedwater passing throughsaid first and second conduits and said low temperature and hightemperature economizers is directed into said high pressure evaporatorabove the condensation temperature thereof,

d. a fourth conduit connecting said high pressure evaporator to saidsuperheater, and

e a fifth conduit connecting said superheater to said steam turbine sothat the steam generated in said high pressure evaporator is passedthrough said fourth conduit to be superheated in passing through saidsuperheater and then directed through said fifth conduit to said steamturbine so that all of the steam generated in this multipressure systemis utilized to generate shaft energy in said steam turbine to drive ashaft driven load,

H. means to add selected quantities of water purifying chemicals to theselected quantity of feedwater being so introduced exclusively to thedeaerator evaporator, to the selected quantity of feedwater beingdirected exclusively to the low pressure evaporator, and to the selectedquantity of feedwater being directed exclusively to the high pressureevaporator, respectively.

10. A powerplant according to claim 9 wherein said third system splitsfrom said second system so that about one-fourth to one-third of thedeaerated feedwater enters said low pressure evaporator and aboutthree-fourths to two-thirds of the deaerated feedwater enters said highpressure evaporator.

11. An unfired, waste-heat-steam turbine combined cycle powerplantwherein waste-heat provides all of the heat to the steam boiler togenerate steam for the steam turbine which is connected to drive a shaftdriven load including:

A. a steam turbine, g

B. a waste-heat stack boiler through which the wasteheat is passed andincluding:

1. a waste-heat stack positioned so that the wasteheat passestherethrough and having an inlet end and an outlet end, Y

2. steam generating means operatively associated withsaid waste-heatstack including:

a. a superheater having tubes extending across said waste-heat stackclosest said inlet end,

b. a high pressure evaporator having tubes extending across saidwaste-heat stack next downstream of the superheater,

. c. a high temperature economizer having tubes extending across saidwaste-heat stack next downstream of said high pressure evaporator,

d. a low pressure evaporator having tubes extending across said wasteheat stack next downstream of said high temperature economizer,

e. a low temperature economizer having tubes extending across said wasteheat stack next downstream of said low pressure evaporator, and

f. a deaerator evaporator having tubes extending across said waste-heatstack next downstream of said low temperature economizer,

C. a condenser connected to said steam turbine to receive steamtherefrom for condensation therein,

D. a feedwater deaerator connected to said condenser to receivecondensate feedwater therefrom,

E. a boiler feed pump connected to said deaerator to receive deaeratedfeedwater therefrom,

F. means to pass deaerated feedwater from said boiler feed pump throughsaid steam generating means and to said steam turbine including threefeedwater flow path conduit systems including:

1. a first flow path conduit system directing a first selected quantityof deaerated feedwater exclusively to the deaerator evaporator from saidboiler feed pump including: i a. a first conduit connecting said boilerfeed pump to said deaerator evaporator,

b. a second conduit conducting low pressure steam generated in saiddeaerator evaporator to said deaerator to serve as the deaerating steamand to be condensed therein for recycling as a saturated mixture throughsaid first and second conduits,

2. a second flow path conduit system directing a second selectedquantity of deaerated feedwater exclusively to the low pressureevaporator including: g}

a. a first conduit extending between said boiler feed pump and said lowtemperature economizer through which a selected quantity of deaeratedfeedwater is passed to be elevated to a selected temperature above thecondensation temperature of the low temperature economizer and the lowpressure evaporator,

b. a second conduit connecting said low temperature economizer to saidlow pressure evaporator to direct said second selected quantity ofdeaerated and selectively heated feedwater at a temperature above thelow pressure evaporator condensation point to the low pressureevaporator, and

c. a conduit connecting said low pressure evaporator to said steamturbine to direct all the steam generated in the low pressure evaporatorto said steam turbine,

3. a third flow path conduit system directing a third selected. quantityof deaerated feedwater from said boiler feed pump exclusively to saidhigh pressure evaporator and including:

a. a first conduit connecting said boiler feedwater pump to said lowtemperature economizer,

b. a second conduit connecting said low temperature economizer to saidhigh temperature economizer in which the deaerated feedwater is heatedto a temperature above the condensation temperature of said highpressure evaporator,

c. a third conduit connecting said high temperature economizer to saidhigh pressure evaporator so that the deaerated feedwater passing throughsaid first and second conduits and said low temperature and hightemperature economizers is directed into said high pressure evaporatorabove the condensation temperature thereof,

d. a fourth conduit connecting said high pressure evaporator to saidsuperheater, and

e. a fifth conduit connecting said superheater to said steam turbine sothat the steam generated in said high pressure evaporator is passedthrough said fourth conduit to be superheated in passing through saidsuperheater and then directed through said fifth conduit to said steamturbine so that all of the steam generated in this multipressure systemis utilized to generate shaft energy in said steam turbine to drive ashaft driven load, a means to a s. 99t.q 91. i%at fitatsrr r r ingchemicals to the selected quantity of feedwater being directedexclusively to the deaerator evaporator, to the selected quantity offeedwater being directed exclusively to the low pressure evaporator, andto the selected quantity of feedwater being directed exclusively to thehigh pressure evaporator, respectively.

12. multipressure steam generating powerplant in cluding a heat recoveryboiler having:

A. a heat duct having an upstream end and a downstream end,

B. a high pressure evaporator having tubes in said heat duct at anupstream station,

C. a low pressure evaporator having tubes in said heat duct at adownstream station, D. an intermediate pressure evaporator having tubesin said heat duct at a station between said high pressure evaporator andsaid low pressure evaporator,

E. means to direct a first quantity of deaerated feedwater exclusivelyto said low pressure evaporator,

F. means to direct a second quantity of deaerated feedwater exclusivelyto said intermediate pressure evaporator,

G. means to direct a third quantity of deaerated feedwater exclusivelyto said high pressure evaporator, and i H. means to optimally chemicallytreat said deaerated feedwater exclusively entering each of said low,intermediate, and high pressure evaporators.

13. A multipressure steam generating powerplant including a heatrecovery boiler having:

A. a heat duct having an upstream end and a downstream end,

B. a high pressure evaporator having tubes in said heat duct at anupstream station,

C. a low pressure evaporator having tubes insaid heat duct at adownstream station,

D. an intermediate pressure evaporator having tubs in said heat duct ata station between said high pressure evaporator and said low pressureevaporator,

E. means todirect a total quantity of deaerated feedwater so that afirst portionthereof flows exclusively to said low pressure evaporator,so that a second portion thereof flows exclusively to said inter.mediate pressure evaporator, and so that the remainder thereof flowsexclusively to said high pressure evaporator, and

F. means to optimally chemically treat the deaerated feedwater beingconducted exclusively into each of said low, intermediate, and highpressure evaporatOI'S.

ew V UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent -No. 3769 795 Dated November 6 19 73 Inventor(s) ERIC G. RORSTROM It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

o In the" heading of the patent please delete "Eric G. Rostrom" andinsert '-Eric G. Rorstr0m-- In the Claims Claim 1, column 7, line 20Delete "burbine" and insert turbine-- Claim 13, column 14, line 50Delete "tubs'Y a'nd insert --tubes-- Signed and sealed this 23rd day ofApril 197E.

(SEAL) I Attest:

EDWARD I"'I.FLETGHER$,JRE C. MARSHALL DANN Commissioner of PatentsAttesting Officer

1. A combined gas turbine-steam turbine cycle powerplant wherein theexhaust gases of the gas turbine provide all of the heat to the steamboiler to generate steam for the steam burbine which is connected todrive a shaft driven load including: A. a gas turbine engine, B. a steamturbine engine, C. an exhaust stack boiler through which the gas turbineengine exhaust gases are passed and including:
 1. an exhaust stackpositioned so that the exhaust gases from said gas turbine engine passtherethrough and having an exhaust gas inlet end and an exhaust gaSoutlet end,
 2. steam generating means operatively associated with saidexhaust stack including: a. a superheater having tubes extending acrosssaid exhaust stack closest said exhaust gas inlet end, b. a highpressure evaporator having tubes extending across said exhaust stacknext downstream of the superheater, c. a high temperature economizerhaving tubes extending across said exhaust stack next downstream of saidhigh pressure evaporator, d. a low pressure evaporator having tubesextending across said exhaust stack next downstream of said hightemperature economizer, e. a low temperature economizer having tubesextending across said exhaust stack next downstream of said low pressureevaporator, and f. a deaerator evaporator having tubes extending acrosssaid exhaust gas stack next downstream of said low temperatureeconomizer, D. means to pass feedwater through said steam generatingmeans including three feedwater flow path conduit systems including: 1.a first flow path conduit system directing a first selected quantity offeedwater exclusively to the deaerator evaporator at a selectedtemperature so that the feedwater being passed through said deaeratorevaporator is above the temperature of the condensation point of theexhaust gases passing over the deaerator evaporator,
 2. a second flowpath conduit system passing a second selected quantity of feedwaterexclusively through said low temperature economizer and then into saidlow pressure evaporator so that the temperature of the feedwater beingpassed through both is above the condensation point of the exhaust gasesbeing passed thereover, and
 3. a third flow path conduit systemdirecting a third selected quantity of feedwater from said lowtemperature economizer exclusively through said high temperatureeconomizer and said high pressure evaporator such that the temperatureof the feedwater passing through both is above the condensation point ofthe exhaust gases passing thereover, E. means to extract steam from saidhigh pressure evaporator and pass it through said superheater andconduct said superheated steam to a high pressure station in the steamturbine, F. means to extract steam from said low pressure evaporator anddirect it to a low pressure station in said steam turbine so as tocooperate with said superheated steam to power said steam turbine todrive said shaft driven load, and G. means to add selected quantities ofwater purifying chemicals to the selected quantity of feedwaterintroduced exclusively to the deaerator evaporator, to the selectedquantity of feedwater being directed exclusively to the low pressureevaporator, and to the selected quantity of feedwater being directedexclusively to the high pressure evaporator, respectively.
 2. steamgenerating means operatively associated with said waste-heat stackincluding: a. a superheater having tubes extending across saidwaste-heat stack closest said inlet end, b. a high pressure evaporatorhaving tubes extending across said waste-heat stack next downstream ofthe superheater, c. a high temperature economizer having tubes extendingacross said waste-heat stack next downstream of said high pressureevaporator, d. a low pressure evaporator having tubes extending acrosssaid waste heat stack next downstream of said high temperatureeconomizer, e. a low temperature economizer having tubes Extendingacross said waste heat stack next downstream of said low pressureevaporator, and f. a deaerator evaporator having tubes extending acrosssaid waste-heat stack next downstream of said low temperatureeconomizer, C. a condenser connected to said steam turbine to receivesteam therefrom for condensation therein, D. a feedwater deaeratorconnected to said condenser to receive condensate feedwater therefrom,E. a boiler feed pump connected to said deaerator to receive deaeratedfeedwater therefrom, F. means to pass deaerated feedwater from saidboiler feed pump through said steam generating means and to said steamturbine including three feedwater flow path conduit systems including:2. steam generating means operatively associated with said exhaust stackincluding: a. a superheater having tubes extending across said exhauststack closest said exhaust gas inlet end, b. a high pressure evaporatorhaving tubes extending across said exhaust stack next downstream of thesuperheater, c. a high temperature economizer having tubes extendingacross said exhaust stack next downstream of said high pressureevaporator, d. a low pressure evaporator having tubes extending acrosssaid exhaust stack next downstream of said high temperature economizer,e. a low temperature economizer having tubes extending across saidexhaust stack next downstream of said low pressure evaporator, and f. adeaerator evaporator having tubes extending across said exhaust gasstack next downstream of said low temperature economizer, D a condenserconnected to said steam turbine to receive steam therefrom forcondensation therein, E a feedwater deaerator connected to saidcondenser to receive condensate feedwater therefrom, F a boiler feedpump connected to said deaerator to receive deaerated feedwatertherefrom, G means to pass deaerated feedwater from said boiler feedpump through said steam generating means and to said steam turbineincluding three feedwater flow path conduit systems including: 1 a firstflow path conduit system directing a first selected quantity ofdeaerated feedwater exclusively to the deaerator evaporator from saidboiler feed pump including: a. a first conduit connecting said boilerfeed pump to said deaerator evaporator, b. a second conduit conductinglow pressure steam generated in said deaerator evaporator to saiddeaerator to serve as the deaerating steam and to be condensed thereinfor recycling as a saturated mixture through said first and secondconduits,
 2. a second flow path conduit system directing a secondselected quantity of deaerated feedwater exclusively to the low pressureevaporator including: a. a first conduit extending between said boilerfeed pump and said low temperature economizer through which a selectedquantity of deaerated feedwater is passed to be elevated to a selectedtemperature above the condensation temperature of the low temperatureeconomizer and the low pressure evaporator, b. a second conduitconnecting said low temperature economizer to said low pressureevaporator to direct said second selected quantity of deaerated andselectively heated feedwater at a temperature above the low pressureevaporator condensation point to the low pressure evaporator, and c. aconduit connecting said low pressure evaporator to said steam turbine todirect all the steam generated in the low pressure evaporator to saidsteam turbine,
 2. a second flow path conduit system passing a secondselected quantity of feedwater exclusively through said low temperatureeconomizer and then into said low pressure evaporator so that thetemperature of the feedwater being passed through both is above thecondensation point of the waste-heat gases being passed thereover, and2. A powerplant according to claim 1 and including: A. a condenserconnected to said turbine to receive steam therefrom for condensationtherein, B. a feedwater deaerator positioned between said condenser andsaid deaerator evaporator, and C. a boiler feed pump positioned betweensaid deaerator and said three feedwater flow path conduit systems so asto pump deaerated boiler feedwater therethrough.
 2. a second flow pathconduit system passing a second selected quantity of feedwaterexclusively through said low temperature economizer and then into saidlow pressure evaporator so that the temperature of the feedwater beingpassed through both is above the condensation point of the exhaust gasesbeing passed thereover, and
 2. steam generating means operativelyassociated with said exhaust stack including: a. a superheater havingtubes extending across said exhaust stack closest said exhaust gas inletend, b. a high pressure evaporator having tubes extending across saidexhaust stack next downstream of the superheater, c. a high temperatureeconomizer having tubes extending across said exhaust stack nextdownstream of said high pressure evaporator, d. a low pressureevaporator having tubes extending across said exhaust stack nextdownstream of said high temperature economizer, e. a low temperatureeconomizer having tubes extending across said exhaust stack nextdownstream of said low pressure evaporator, and f. a deaeratorevaporator having tubes extending across said exhaust gas stack nextdownstream of said low temperature economizer, D. means to passfeedwater through said steam generating means including three feedwaterflow path conduit systems including:
 3. a third flow path conduit systemdirecting a third selected quantity of feedwater from said lowtemperature economizer exclusively through said high temperatureeconomizer and said high pressure evaporator such that the temperatureof the feedwater passing through both is above the condensation point ofthe exhaust gases passing thereover, E. means to extract steam from saidhigh pressure evaporator and pass it through said superheater andconduct said superheated steam to a high pressure station in the steamturbine, F. means to extract steam from said low pressure evaporator anddirect it to a low pressure station in said steam turbine so as tocooperate with said superheated steam to power said steam turbine todrive said shaft driven load, and G. means to add selected quantities ofwater purifying chemicals to the selected quantity of feedwaterintroduced exclusively to the deaerator evaporator, to the selectedquantity of feedwater being directed exclusively to the low pressureevaporator, and to the selected quantity of feedwater being directedexclusively to the high pressure evaporator, respectively.
 3. Anunfired, waste-heat-steam turbine cycle powerplant wherein waste-heatprovides all of the heat to the steam boiler to generate steam for thesteam turbine which is connected to drive a shaft driven load including:A. a steam turbine, B. a waste-heat stack boiler through which thewaste-heat is passed and including: 1 a waste-heat stack positioned sothat the waste-heat passes therethrough and having an inlet end and anoutlet end, 2 steam generating means operatively associated with saidwaste-heat stack including: a. a superheater having tubes extendingacross said waste-heat stack closest said inlet end, b. a high pressureevaporator having tubes extending across said waste-heat stack nextdownstream of the superheater, c. a high temperature economizer havingtubes extending across said waste-heat stack next downstream of saidhigh pressure evaporator, d. a low pressure evaporator having tubesextending across said waste-heat stack next downstream of said hightemperature economizer, e. a low temperature economizer having tubesextending across said waste-heat stack next downstream of said lowpressure evaporator, and f. a deaerator evaporator having tubesextending across said waste-heat stack next downstream of said lowtemperature economizer, C. means to pass feedwater through said steamgenerating means including three feedwater flow path conduit systemsincluding:
 3. a third flow path conduit system directing a thirdselected quantity of feedwater from said low temperature economizerexclusively through said high temperature economizer and said highpressure evaporator such that the temperature of the feedwater passingthrough both is above the condensation point of the waste-heat gasespassing thereover, D. means to extract steam from said high pressureevaporator and pass it through said superheater and conduct saidsuperheated steam to a high pressure station in the steam turbine, E.means to extract steam from said low pressure evaporator and direct itto a low pressure station in said steam turbine so as to cooperate withsaid superheated steam to power said steam turbine to drive said shaftdriven load, and F. means to add selected quantities of water purifyingchemicals to the selected quantity of feedwater introduced exclusivelyto the deaerator evaporator, to the selected quantity of feedwater beingdirected exclusively to the low pressure evaporator, and to the selectedquantity of feedwater being directed exclusively to the high pressureevaporator, respectively.
 3. a third flow path conduit system directinga third selected quantity of deaerated feedwater from said boiler feedpump exclusively to said high pressure evaporator and including: a. afirst conduit connecting said boiler feedwater pump to said lowtemperature economizer, b. a second conduit connecting said lowtemperature economizer to said high temperature economizer in which thedeaerated feedwater is heated to a temperature above the condensationtemperature of said high pressure evaporator, c. a third conduitconnecting said high temperature economizer to said high pressureevaporator so that the deaerated feedwater passing through said firstand second conduits and said low temperature and high temperatureeconomizers is directed into said high pressure evaporator above thecondensation temperature thereof, d. a fourth conduit connecting saidhigh pressure evaporator to said superheater, and e a fifth conduitconnecting said superheater to said steam turbine so that the steamgenerated in said high pressure evaporator is passed through said fourthconduit to be superheated in passing through said superheater and thendirected through said fifth conduit to said steam turbine so that all ofthe steam generated in this multipressure system is utilized to generateshaft energy in said steam turbine to drive a shaft driven load, H meansto add selected quantities of water purifying chemicals to the selectedquantity of feedwater being so introduced exclusively to the deaeratorevaporator, to the selected quantity of feedwater being directedexclusively to the low pressure evaporator, and to the selected quantityof feedwater being directed exclusively to the high pressure evaporator,respectively.
 3. a third flow path conduit system directing a thirdselected quantity of deaerated feedwater from said boiler feed pumpexclusively to said high pressure evaporator and including: a. a firstconduit connecting said boiler feedwater pump to said low temperatureeconomizer, b. a second conduit connecting said low temperatureeconomizer to said high temperature economizer in which the deaeratedfeedwater is heated to a temperature above the condensation temperatureof said high pressure evaporator, c. a third conduit connecting saidhigh temperature economizer to said high pressure evaporator so that thedeaerated feedwater passing through said first and second conduits andsaid low temperature and high temperature economizers is directed intosaid high pressure evaporator above the condensation temperaturethereof, d. a fourth conduit connecting said high pressure evaporator tosaid superheater, and e. a fifth conduit connecting said superheater tosaid steam turbine so that the steam generated in said high pressureevaporator is passed through said fourth conduit to be superheated inpassing through said superheater and then directed through said fifthconduit to said steam turbine so that all of the steam generated in thismultipressure system is utilized to generate shaft energy in said steamturbine to drive a shaft driven load, G means to add selected quantitiesof water purifying chemicals to the selected quantity of feedwater beingdirected exclusively to the deaerator evaporator, to the selectedquantity of feedwater being directed exclusively to the low pressureevaporator, and to the selected quantity of feedwater being directedexclusively to the high pressure evaporator, respectively.
 4. Amultipressure steam generating powerplant including a heat recoveryboiler having: A a heat duct having an upstream end and a downstreamend, B a high pressure evaporator having tubes in said heat duct at anupstream station, C a low pressure evaporator having tubes in said heatduct at a downstream station, D first feedwater conduit means connectedto provide a selected quantity of feedwater exclusively to said lowpressure evaporator and including:
 5. A powerplant according to claim 4and including means to deaerate the feedwater to be passed through saidfirst and second conduit means.
 6. A powerplant according to claim 5wherein said feedwater deaeration means includes: A a deaeratorevaporator positioned in said heat duct downstream of said low pressureevaporator, B a fluid-to-fluid deaerator, and C conduits connecting saiddeaerator to said deaerator evaporator to conduct feedwater from saiddeaerator to said deaerator evaporator to generate low pressure steAmtherein and to conduct said steam back to said deaerator to heat anddeaerate the entering feedwater.
 7. A powerplant according to claim 6and including: A. means located in said first feedwater conduit means toheat the deaerated feedwater passing therethrough to a point at whichthe deaerated feedwater will heat the low pressure evaporator above thecondensation temperature of the waste-heat gas passing thereover, and B.means located in said second feedwater conduit means to heat thedeaerated feedwater passing therethrough to a point at which thedeaerated feedwater will heat the high pressure evaporator to atemperature above the condensation temperature of the waste-heat gaspassing thereover.
 8. A powerplant according to claim 5 wherein saidfeedwater deaerator includes a fluid-to-fluid deaerator positionedexternally of the heat stack and a deaerator evaporator having tubes insaid heat stack at a station downstream of said low pressure evaporatorand conduit means connecting said deaerator and said deaeratorevaporator so that the low pressure steam generated in said deaeratorevaporator is directed to said deaerator so as to heat the feedwaterentering the deaerator to deaerate the feedwater and so that thesaturated mixture of feedwater and steam accumulated in said deaeratorafter said mixing will be passed in part to said deaerator evaporator,in part to said low pressure evaporator and in part to said highpressure evaporator.
 9. A gas turbine-steam turbine unfired, combinedcycle powerplant wherein the exhaust gases of the gas turbine provideall of the heat to the steam boiler to generate steam for the steamturbine which is connected to drive a shaft driven load including: A. agas turbine engine, B. a steam turbine engine, C. a waste-heat boilerthrough which the gas turbine engine exhaust gases are passed andincluding:
 10. A powerplant according to claim 9 wherein said thirdsystem splits from said second system so that about one-fourth toone-third of the deaerated feedwater enters said low pressure evaporatorand about three-fourths to two-thirds of the deaerated feedwater enterssaid high pressure evaporator.
 11. An unfired, waste-heat-steam turbinecombined cycle powerplant wherein waste-heat provides all of the heat tothe steam boiler to generate steam for the steam turbine which isconnected to drive a shaft driven load including: A. a steam turbine, B.a waste-heat stack boiler through which the waste-heat is passed andincluding:
 12. multipressure steam generating powerplant including aheat recovery boiler having: A. a heAt duct having an upstream end and adownstream end, B. a high pressure evaporator having tubes in said heatduct at an upstream station, C. a low pressure evaporator having tubesin said heat duct at a downstream station, D. an intermediate pressureevaporator having tubes in said heat duct at a station between said highpressure evaporator and said low pressure evaporator, E. means to directa first quantity of deaerated feedwater exclusively to said low pressureevaporator, F. means to direct a second quantity of deaerated feedwaterexclusively to said intermediate pressure evaporator, G. means to directa third quantity of deaerated feedwater exclusively to said highpressure evaporator, and H. means to optimally chemically treat saiddeaerated feedwater exclusively entering each of said low, intermediate,and high pressure evaporators.
 13. A multipressure steam generatingpowerplant including a heat recovery boiler having: A. a heat ducthaving an upstream end and a downstream end, B. a high pressureevaporator having tubes in said heat duct at an upstream station, C. alow pressure evaporator having tubes in said heat duct at a downstreamstation, D. an intermediate pressure evaporator having tubs in said heatduct at a station between said high pressure evaporator and said lowpressure evaporator, E. means to direct a total quantity of deaeratedfeedwater so that a first portion thereof flows exclusively to said lowpressure evaporator, so that a second portion thereof flows exclusivelyto said intermediate pressure evaporator, and so that the remainderthereof flows exclusively to said high pressure evaporator, and F. meansto optimally chemically treat the deaerated feedwater being conductedexclusively into each of said low, intermediate, and high pressureevaporators.